Extrusion cooking of cereals is a complex process, regarding a wide range of food products (snack-foods, baby-foods, cereals for breakfast and pasta). in this work, an analysis of variance (ANOVA) on the extrusion cooking process for cereals in a co-rotating twin-screw extruder was carried out, using a finite-element fluid dynamic simulation model, to study shear rate, residence time and mixing index inside the extruder, varying temperature, screw rotation velocity, flow rate and extruder geometry. Besides, the significance analysis, carried out in this study, have shown several aspects of the process under investigation: (i) the interdependence between shear rate, screw rotation velocity and screw axis ratio seems very strong; (ii) the significance of the effects on shear rate of the variations of temperature and flow rate appears less meaningful; (iii) the influence on the residence time of the flow rate and screw axis ratio is more meaningful respect to the screw speed and temperature. The numerical simulations have revealed numerous aspects that can be used to improve the extrusion process: the flow temperature can be varied without modifying the gelatinization of material that is mainly influenced by screw rotation velocity and screw axis ratio. (c) 2004 Elsevier Ltd. All rights reserved.